The present invention relates to a magnetic storage system, and more particularly to a signal processing circuit employing a novel analog to digital (A/D) conversion system that is preferably used for a signal processing circuit that uses digital signals of a magnetic storage system and to a magnetic storage system using the same circuit.
Studies have been made for employing partial response (PR) signal transmission technology in the field of communications as a read/write system for magnetic storage systems such as magnetic disk units. According to this technology, the recording signals are recorded while compressing the band of the recording signals, and during the reproduction, the waveforms inclusive of read/write characteristics are equalized, and the signals of a narrow band are reproduced on multiple levels.
The PR waveforms can be processed through a simply constituted circuit when the processing is carried out in the stage succeeding the equalizer. Here, however, the equalizer requires Nyquist equalization, leaving such problems as retarded convergence and increased equalization error. On the other hand, when the PR waveform processing is carried out in the stage preceding the equalizer by a method disclosed in, for example, U.S. Pat. No. 5,060,088, the automatic equalizer has a lessened load and the equalization is improved in regard to convergence and error.
FIG. 11 of the present application shows a conventional signal processing circuit for the case when the PR waveform processing is carried out in the stage preceding the equalizer. As shown in FIG. 11, the equalization that corresponds to the PR waveform processing is carried out by an analog fixed equalizer 6 in the stage preceding the automatic equalizer. A change in the characteristics of a read/write system caused by track position and the like of a magnetic disk 1 is adjusted for its gain through an automatic gain control circuit (AGC circuit) 4 and is digitized through an A/D converter 7. Then, by using known data recorded in advance on the magnetic disk 1, the characteristics of a digital equalizer are absorbed by automatic equalization characteristics of a compensative circuit 10. The change in the characteristics is then discriminated by a Viterbi decoder (discriminator) 9 in the succeeding stage. The automatic equalization system described above allows error due to the characteristics of the signal processing circuit to a great degree, but offers an increased degree of freedom for circuit design and reduces the cost of the storage system
However, in the above prior art, the analog fixed equalizer 6 that performs the PR waveform processing requires complex processing of characteristics including slimming of waveforms, notching at a predetermined frequency and removal noise. For this purpose, therefore, such circuit components are required as an operational amplifier, a capacitor of a large capacity, an inductance, and the like. Moreover, an AGC circuit 4 composed of analog bipolar transistors is employed to output a suitable digital signal from an A/D converter in a stage that precedes the digital equalizer 8, in order to adjust the amplitude which is necessary for the digitization. These analog circuits and the outputting elements must be formed in an integrated manner involving great difficulty. In addition, an increase in the consumption of electric power and in the mounting area is not avoidable.